Multi-particle and high-dimension controlled order rearrangement encryption protocols

Based on controlled order rearrange encryption (CORE) for quantum key distribution using EPR pairs [Fu.G. Deng, G.L. Long, Phys. Rev. A 68, 042315 (2003)], we propose generalized controlled order rearrangement encryption (GCORE) protocols of N qubits and N qutrits, and concretely display them in cases using 3-qubit, 2-qutrit maximally entangled basis states. We further show that our protocols will become safer with an increase in dimensions and number of particles. Moreover, we carry out the security analysis using quantum covariant cloning machine. Although the applications of the generalized scheme need to be further studied, GCORE has many distinct features such as large capacity and high efficiency.     

Scheme for implementing perfect quantum dense coding with three-atom W-class state in cavity QED

We propose an experimentally feasible scheme of implementing perfect quantum dense coding with three-atom W-class state in cavity QED. In this scheme atoms interact simultaneously with a highly detuned cavity field and the cavity is only virtually excited, thus the scheme is insensitive to the cavity decay, which is very important in view of experiment. Moreover, we also propose a scheme of transmitting three bits of classical information by sending one qubit and one classical bit with 3-qubit W-class and GHZ states.     

A revised controlled deterministic secure quantum communication with five-photon entangled state

A revised controlled deterministic secure quantum communication protocol using five-photon entangled state is proposed. It amends the security loopholes pointed by Qin et al. in [S.J. Qin, Q.Y. Wen, L.M. Meng, F.C. Zhu, Opt. Commun. 282 (2009) 2656] in the original protocol proposed by Xiu et al. in [X.M. Xiu, L. Dong, Y.J. Gao, F. Chi, Opt. Commun. 282 (2009) 333]. The security loopholes are solved by using order rearrangement of transmission photons and two-step security test.     

Cryptanalysis of multiparty controlled quantum secure direct communication using Greenberger-Horne-Zeilinger state

We analyze the security of multiparty controlled quantum secure direct communication using Greenberger-Horne-Zeilinger (GHZ) state. It is shown that the receiver, using a special property of GHZ state, can illegally obtain 33.3% of the sender’s secret without any controller’s permission. The attack strategy is demonstrated in detail and an improvement of this protocol is discussed. The idea of this attack might be instructive for the cryptanalysis of quantum cryptographic protocols.     

Quantum cryptography using partially entangled states

We show that non-maximally entangled states can be used to build a quantum key distribution (QKD) scheme where the key is probabilistically teleported from Alice to Bob. This probabilistic aspect of the protocol ensures the security of the key without the need of non-orthogonal states to encode it, in contrast to other QKD schemes. Also, the security and key transmission rate of the present protocol is nearly equivalent to those of standard QKD schemes and these aspects can be controlled by properly harnessing the new free parameter in the present proposal, namely, the degree of partial entanglement. Furthermore, we discuss how to build a controlled QKD scheme, also based on partially entangled states, where a third party can decide whether or not Alice and Bob are allowed to share a key.     

Novel Quantum Secret Sharing and Controlled Communication Schemes Based on Einstein-Podolsky-Rosen Correlations

Employing quantum registers, we first proposed a novel （2, 3） quantum threshold scheme based on Einstein- Podolsky Rosen （EPR） correlations in this letter. Motivated by the present threshold scheme, we also propose a controlled communication scheme to transmit the secret message with a controller. In the communication protocol, the encoded quantum message carried by particles sequence, is transmitted by legitimate communicators.     

Improving the total efficiency of quantum key distribution by comparing Bell states

A protocol for quantum key distribution by comparing Bell states [G. Gao, Opt. Commun. 281 (2008) 876] is recently proposed by Gan Gao. Gan Gao claimed that his protocol has the advantage of high total efficiency and its total efficiency is 50%. In this paper, by giving a little modification to the original one, we introduce an improved version of Gao’s protocol, which can make the total efficiency of the communication come up to 100%.     

Quantum bit string commitment protocol using polarization of mesoscopic coherent states

In this work, we propose a quantum bit string commitment protocol using polarization of mesoscopic coherent states. The protocol is described and its security against brute force and quantum cloning machine attack is analyzed.     

Controlled quantum secure direct communication using a non-symmetric quantum channel with quantum superdense coding

We present a controlled quantum secure direct communication protocol that uses a 2-dimensional Greenberger–Horne–Zeilinger (GHZ) entangled state and a 3-dimensional Bell-basis state and employs the high-dimensional quantum superdense coding, local collective unitary operations and entanglement swapping. The proposed protocol is secure and of high source capacity. It can effectively protect the communication against a destroying-travel-qubit-type attack. With this protocol, the information transmission is greatly increased. This protocol can also be modified, so that it can be used in a multi-party control system.     

Scalable Quantum Secret Sharing Extended from Quantum Key Distribution

We suggest a general approach for extending quantum key distribution （Q, KD） protocols possessing discrete rotational symmetry into quantum secret sharing （QSS） schemes among multiparty, under certain conditions. Only local unitary operations are required for this generalization based on the almost mature technologies of Q, KD. Theoretically, the number of the participating partners can be arbitrary high. As an application of this method, we propose a fault-tolerant QSS protocol based on a fault-tolerant QKD implementation. The 6-state protocol is also discussed.     

Performance of Differential-Phase-Shift Keying Protocol Applying 1310nm Up-Conversion Single-Photon Detector

The performance of the differential-phase-shift keying （DPSK） protocol applying a 1310nm up-conversion singlephoton detector is analysed. The error rate and the communication rate as a function of distance for three quantum key distribution protocols, the Bennett-Brassard 1984, the Bennett-Brassard -Mermin 1992, and the DPSK, are presented. Then we compare the performance of these three protocols using the 1310 nm up-conversion detector. We draw the conclusion that the DPSK protocol applying the detector has significant advantage over the other two protocols. Longer transmission distance and lower error rate can be achieved.     

Quantum oblivious transfer with an untrusted third party

Given the Mayers–Lo–Chau (MLC) no-go theorem, unconditionally secure quantum bit commitment (QBC) is impossible and hence quantum oblivious transfer (QOT) based on QBC is insecure. In this paper, we propose a secure all-or-nothing QOT protocol and a one-out-of-two QOT protocol respectively. The unique merit of the proposed protocols lies in that it is not based on QBC but based on an untrusted third party. Moreover, the proposed protocols do not violate Lo's no-go theorem so that their security can be achieved.     

Entanglement-assisted quantum logic gates for two remote qubits

We propose a protocol to realize quantum logic gates for two remote qubits via entanglement swapping. According to the scheme of quantum repeater presented by H.-J. Briegel et al., we can complete long-distance communication and computation. Compared with previous schemes through noisy channels, our protocol can overcome the limitation that error probability scales exponentially with the length of the channel. We illustrate this protocol in cavity QED system, but the idea can also be realized in other physical systems.     

Probabilistic Controlled Teleportation of a Triplet W State with Combined Channel of Non-Maximally Entangled Einstein-Podolsky-Rosen and Greenberger-Horne-Zeilinger States

A scheme for probabilistic controlled teleportation of a triplet W state using combined non-maximally entangled channel of two Einstein-Podolsky-Rosen （EPR） states and one Creenberger-Horne-Zeilinger （CHZ） state is proposed. In this scheme, an （m ＋ 2）-qubit CHZ state serves not only as the control parameter but also as the quantum channel. The m control qubits are shared by m supervisors. With the aid of local operations and individual measurements, including Bell-state measurement, Von Neumann measurement, and mutual classical communication etc., Bob can faithfully reconstruct the original state by performing relevant unitary transformations. The total probability of successful teleportation is only dependent on channel coefficients of EPR states and GHZ, independent of the number of supervisor m. This protocol can also be extended to probabilistic controlled teleportation of an arbitrary N-qubit state using combined non-maximally entangled channel of N- 1 EPR states and one （m ＋ 2）-qubit GHZ.     

Random unitary qubit channels: entropy relations,private quantum channels and non-malleability

Channels encrypting quantum bits by the application of randomly chosen unitary operators are studied. Quantities based on averages of linear entropies which characterize certain aspects of the encoding quality and the non-malleability of the channels are introduced. The relation between the entropy of the classical key and the choice of the encryption operators with the behaviour of these properties is discussed. The extension of exact private quantum channels in order to improve non-malleability via additional encryption operators is considered.     

Teleportation of Mixture of Diagonal Bell States via Bound Entangled States

We propose a protocol for teleportation of arbitrary mixture of diagonal Bell states, it is shown that the channel can be constructed with either pure maximally entangled states or mixed bound entangled states. We also present protocols to realize the controlled teleportation of mixture of diagonal Bell states via multi-particle mixed states. Our results show that bound entangled states are also important and useful resources in quantum communication tasks.     

Improving the security of secure quantum telephone against an attack with fake particles and local operations

The security of the secure quantum telephone protocol [X.J. Wen, Y. Liu, N.R. Zhou, Opt. Commun. 275 (2007) 278] is analyzed. It is shown that an eavesdropper can attack the communicators’ messages by using fake particles and local operations. Moreover, the essential reasons of the information leakage are discussed. Finally, a simple improvement of the secure quantum telephone protocol is proposed.     

A Modified Protocol of Quantum Key Distribution Based on Entanglement Swapping

By comparing Cabello＇s addendum to his quantum key distribution protocol [Phys. Rev. A 64 （2001） 024301], we propose a more convenient modified protocol based on the entanglement swapping which is secure against the eavesdropping strategy addressed by Zhang et al. [Phys. Rev. A 63 （2001）036301] and other existing types of attack.     

Scalable quantum computing in decoherence-free subspaces with Cooper-pair box qubits

We theoretically propose a feasible scheme to perform quantum computing in decoherence-free subspaces (DFSs) with Cooper-pair box (CPB) qubits arrayed in a circuit QED architecture. Based on the cavity-bus assisted interaction, the selective and controllable interqubit couplings occur only by adjusting the individual gate pulses, by which we obtain the scalable DFS-encoded universal quantum gates to resist certain collective noises. Further analysis shows the protocol may implement the scalable fault-tolerant quantum computing with current experimental means.     

Eavesdropping on secure quantum telephone protocol with dishonest server

The crucial issue of quantum communication protocol is its security. In this paper, we show that in secure quantum telephone protocol proposed by Wen et al. [X. Wen et al., Opt. Commun. 275 (2007) 278-282] the dishonest server can obtain full information of the communication with zero risk of being detected.